Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$242.58	12.545%	$273.0117	$273.01	$273.00	$273.00
Purchase #2	$59.77	12.159%	$67.0374	$67.04	$67.05	$67.00
Purchase #3	$11.89	10.841%	$13.179	$13.18	$13.20	$13.20
Purchase #4	$116.77	7.427%	$125.4425	$125.44	$125.45	$125.40
Purchase #5	$105.47	3.326%	$108.9779	$108.98	$109.00	$109.00
Purchase #6	$209.39	6.153%	$222.2738	$222.27	$222.25	$222.30
Purchase #7	$174.54	12.641%	$196.6036	$196.60	$196.60	$196.60
7 purchase totals =	$920.41		$1,006.5259	$1,006.52	$1,006.55	$1,006.50